Febrile convulsions
An 8-month-old baby has been referred to you by the Accident and Emergency Department with the first episode of febrile convulsion.
He has been coryzal over the last couple of days with temperature spikes up to 38C.
The episode lasted for five minutes; the baby felt hot then, and following recovery, he remained well.
Bottom line
Febrile seizures are benign.
They typically occur in children six months – 6 years, and they can be either simple or complex (duration > 15 minutes, multiple seizures over a 24-hour period, focal neurology).
The risk of recurrence is 30%
The risk of developing epilepsy following a simple febrile seizure is low but significantly higher with complex febrile convulsions.
There is no evidence for the use of regular antipyretics to prevent recurrence during an acute febrile episode.
Part of the management is parental education on managing future episodes at home and recognising signs that the child needs urgent medical attention.
What is a febrile convulsion?
A febrile convulsion is a seizure associated with fever (at least 38C) without central nervous system infection or any electrolyte imbalance in a young child. By definition, febrile seizures occur in children between 6 months and 6 years of age. The median age of onset is 18 months, and half of the children are between 12 and 30 months old.
What are the features of a febrile convulsion?
The most common type of febrile seizure (75%) is a simple febrile seizure. It is usually a brief, generalized tonic-clonic seizure that occurs with the onset of a rising temperature. In 87% of children, the febrile seizure lasts less than 10 minutes.
A complex febrile seizure is defined by at least one of the following criteria:
Duration of the seizure longer than 15 minutes
Multiple seizures within the last 24 hours
Presence of focal seizures
Febrile status epilepticus (> 30 minutes duration) occurs in only 5% of the paediatric population.
What causes febrile convulsions?
The hypothalamus is responsible for homeostatic core temperature regulation. It is still developing in a young child, so it is more susceptible to rapid rises in body temperature. A febrile seizure represents the meeting point of a lower threshold for seizures and a trigger—the fever.
Mutations in sodium ion channel genes and neurotransmitter genes (e.g. gamma-aminobutyric acid) have been identified in children with febrile seizures. These findings suggest the hypothesis of neuronal hyperexcitability to certain triggers.
Fever is the main trigger for febrile seizures. Viral infections are the main cause of fever. HHV-6 in roseola accounts for 20% of the cases presenting with the first episode of simple febrile seizures
What often do febrile convulsions recur?
This is a commonly asked question by the parents. 30% of the children with a first episode of febrile convulsion will have a recurrence in the future. The following are risk factors associated with a higher risk of recurrence:
- Onset before the 18 months
- Shorter duration of fever (<1 hour) before the onset of the seizure
- Lower temperature close to 38oC
- Family history of febrile seizures
Will children who have febrile convulsions develop epilepsy?
The vast majority of children presenting with febrile convulsions do not develop epilepsy.
The following are risk factors for developing afebrile seizures:
- Complex febrile seizures
- Presence of neurodevelopmental abnormality
- Family history of epilepsy
- Prolonged febrile seizures
Children with no risk factors have a 2.4% risk of developing afebrile seizures by the age of 25 compared with 1.4% per cent for the general paediatric population. The risk is increased to 49% when all three component features of complex febrile convulsions are present.
What tests do we need to do in a child who has had a febrile convulsion?
The investigations done on a child with a fever should be directed by the severity of the illness and the suspected underlying condition.
For a child presenting with a simple febrile seizure and who is otherwise well, a careful history and systems examination should reveal the cause. A urine sample should be obtained to rule out urinary tract infections. Routine blood tests in children with simple febrile seizures are not recommended.
Consider the following tests in cases with diagnostic uncertainty or when the child appears to be unwell:
- Blood testing for FBC, urea and electrolytes and CRP
- CXR to look for evidence of chest infection
- Lumbar puncture: if not contraindicated, it should be performed as soon as possible when meningitis or encephalitis is suspected
- Neuroimaging when focal neurology is present
Antibiotic treatment should be given accordingly when there is evidence of bacterial infection. When meningitis/encephalitis is suspected admission to the hospital is required for immediate commencement on intravenous antibiotics (ceftriaxone +/- acyclovir).
Addendum (November 2021): With COVID-19 fluttering around the world, it is worth considering whether it could cause the seizure. Think about protecting yourself and colleagues from the aerosol-spread nasties.
What advice should be given to parents?
The seizures are benign.
There is a 30% chance of them recurring.
There is little evidence behind using antipyretic agents solely to keep temperature down or to prevent future episodes
The management of future episodes (placing the child in the lateral position, avoiding forcing anything into the child’s mouth, ringing an emergency ambulance if a seizure lasts for >5 minutes)
An explanation of signs and symptoms that would imply that the child is unwell (dehydration, petechial spots)
References
Lynette G Saddleir, Ingrid E Scheffer. Febrile seizures. BMJ 2007;334:307-311
Febrile Seizures, NICE Clinical Knowledge Summaries 2008
